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| United States Patent |
5,094,724
|
|
Berg
, et al.
|
March 10, 1992
|
Separation of methylene chloride from the lower formates by extractive
distillation
Abstract
Methylene chloride cannot be completely separated from methyl formate or
ethyl formate by conventional distillation or rectification because of the
minimum boiling azeotrope. Methylene chloride can be readily separated
from methyl formate or ethyl formate by extractive distillation. Typical
effective agents are: for methyl formate, n-butyl acetate and 3-hexanone;
for ethyl formate, isobornyl acetate and 2-heptanone.
| Inventors:
|
Berg; Lloyd (1314 South Third Ave., Bozeman, MT 59715);
Yang; Zuyin (Bozeman, MT)
|
| Assignee:
|
Berg; Lloyd (Bozeman, MT)
|
| Appl. No.:
|
687507 |
| Filed:
|
April 19, 1991 |
| Current U.S. Class: |
203/57; 203/60; 203/62; 203/63; 203/64; 560/248; 570/262 |
| Intern'l Class: |
B01D 003/40; C07C 017/38 |
| Field of Search: |
203/57,60,62,63,64
570/262
560/248
|
References Cited
U.S. Patent Documents
| 2865955 | Dec., 1958 | Ascherl et al. | 560/248.
|
| 3350416 | Oct., 1967 | Binning et al. | 560/248.
|
| 3431181 | Mar., 1969 | Bouniot | 560/248.
|
| 3848007 | Nov., 1974 | Forlano | 570/262.
|
| 3951756 | Apr., 1976 | Dirks et al. | 560/248.
|
| 4036703 | Jul., 1977 | LeRoi et al. | 203/60.
|
| 4083931 | Apr., 1978 | Lee | 560/248.
|
| 4121978 | Oct., 1978 | Becuwe | 203/60.
|
| Foreign Patent Documents |
| 3135280 | Mar., 1983 | DE | 560/248.
|
| 142183 | Jun., 1980 | DD | 203/64.
|
Primary Examiner: Bascomb, Jr.; Wilbur
Claims
We claim:
1. A method for recovering methylene chloride from a mixture of methylene
chloride and methyl formate which comprises distilling a mixture of
methylene chloride and methyl formate in the presence of about one part of
an extractive agent per part of methylene chloride - methyl formate
mixture, recovering the methylene chloride as overhead product and
obtaining the methyl formate and the extractive agent from the stillpot,
wherein said extractive agent consists of one material selected from the
group consisting of methyl acetate, ethyl acetate, isopropyl acetate,
n-propyl acetate, 4-methyl-2-pentanone, 3-pentanone, n-butyl acetate,
isobutyl acetate, mesityl oxide, 3-hexanone, 2-hexanone,
3-methyl-1-butanol, ethyl butyl ketone, 3,3-dimethyl-2-butanone, 2-methyl
pentanone, isoamyl acetate, n-amyl acetate, methyl isoamyl ketone,
propylene glycol dimethyl ether and ethylene glycol methyl ether acetate.
2. A method for recovering methylene chloride from a mixture of methylene
chloride and ethyl formate which comprises distilling a mixture of
methylene chloride and ethyl formate in the presence of about one part of
an extractive agent per part of methylene chloride - ethyl formate
mixture, recovering the methylene chloride as overhead product and
obtaining the ethyl formate and the extractive agent from the stillpot,
wherein said extractive agent consists of one material selected from the
group consisting of n-butyl acetate, isobutyl acetate, n-amyl acetate,
isoamyl acetate, hexyl acetate, isobornyl acetate, ethylene glycol ethyl
ether acetate, mesityl oxide, ethyl butyl ketone, 3,3-dimethyl-2-butanone,
3-methyl-2-butanone, 3-hexanone, 2-heptanone, diisobutyl ketone, methyl
isoamyl ketone, 2,4-pentanedione, diacetone alcohol, propoxypropanol,
butoxypropanol, propylene glycol methyl ether, propyl butyrate, dibutyl
ether, diethylene glycol t-butyl methyl ether, nitromethane,
1-nitropropane and 2-nitropropane.
Description
FIELD OF THE INVENTION
This invention relates to a method for separating methylene chloride from
methyl formate or ethyl formate using certain organic compounds as the
agent in extractive distillation.
DESCRIPTION OF PRIOR ART
Extractive distillation is the method of separating close boiling compounds
from each other by carrying out the distillation in a multiplate
rectification column in the presence of an added liquid or liquid mixture,
said liquid(s) having a boiling point higher than the compounds being
separated. The extractive agent is introduced near the top of the column
and flows downward until it reaches the stillpot or reboiler. Its presence
on each plate of the rectification column alters the relative volatility
of the close boiling compounds in a direction to make the separation on
each plate greater and thus require either fewer plates to effect the same
separation or make possible a greater degree of separation with the same
number of plates. The extractive agent should boil higher than any of the
close boiling liquids being separated and not form minimum azeotropes with
them. Usually the extractive agent is introduced a few plates from the top
of the column to insure that none of the extractive agent is carried over
with the lowest boiling component. This usually requires that the
extractive agent boil about twenty Centigrade degrees or more higher than
the lowest boiling component.
At the bottom of a continuous column, the less volatile components of the
close boiling mixtures and the extractive agent are continuously removed
from the column. The usual methods of separation of these two components
are the use of another rectification column, cooling and phase separation,
or solvent extraction.
Methylene chloride, B.P.=40.degree. C. forms a minimum boiling azeotrope
with methyl formate, B.P.=32.degree. C. at 31.degree. C. containing 20%
methylene chloride. Methylene chloride forms a minimum boiling azeotrope
with ethyl formate, B.P.=54.degree. C. at 39.5.degree. C. containing 77%
methylene chloride. The methylene chloride - formate azeotropes are
impossible to separate by distillation because the relative volatility of
an azeotrope is 1.0. Extractive distillation would be an attractive method
of effecting the separation of methylene chloride from these formates if
agents can be found that (1) will enhance the relative volatility between
methylene chloride and these formates ans (2) are easy to recover, that
is, form no azeotrope with methylene chloride, methyl formate or ethyl
formate and boil sufficiently above these three compounds to make
separation by rectification possible with only a few theoretical plates.
Extractive distillation typically requires the addition of an equal amount
to twice as much extractive agent as the methylene chloride - formate on
each plate of the rectification column. The extractive agent should be
heated to about the same temperature as the plate into which it is
introduced. Thus extractive distillation imposes an additional heat
requirement on the column as well as somewhat larger plates. However this
is less than the increase occasioned by the additional agents required in
azeotropic distillation.
Another consideration in the selection of the extractive distillation agent
is its recovery from the bottoms product. The usual method is by
rectification in another column. In order to keep the cost of this
operation to a minimum, an appreciable boiling point difference between
the compound being separated and the extractive agent is desirable. We
recommend twenty Centigrade degrees or more difference. It is also
desirable that the extractive agent be miscible with the methylene
chloride and the formates otherwise it will form a two phase azeotrope
with it and some other method of separation will have to be employed.
TABLE 1
______________________________________
Effect of Relative Volatility on the
Separation of Methylene Chloride
from Formates at 99% Purity.
Relative
Theoretical
Actual Plates,
Actual Plates,
Volatility
Plates 75% Efficiency
75% Eff., Min. Reflux
______________________________________
1.2 50 67 87
1.3 35 47 61
1.4 27 36 47
1.5 23 31 40
1.6 20 27 35
1.7 17 23 29
______________________________________
The advantage of employinng an effective extractive distillation agent for
this separation is shown in Table 1. When ordinary rectification is used,
87 usual plates of 75% efficiency are required at minimum reflux ratio to
separate methylene chloride from the formates in 99% purity. If extractive
distillation is employed with an agent that converts the relative
volatility to 1.7, only 29 plates are required.
OBJECTIVE OF THE INVENTION
The objects of this invention are to provide a process or method of
azeotropic or extractive distillation that will enhance the relative
volatility of methylene chloride to methyl formate or ethyl formate in
their separation in a rectification column. It is a further object of this
invention to identify organic compounds that are stable, can be separated
from the methylene chloride or formate by rectification with relatively
few plates and can be recycled to the extractive distillation column with
little decomposition.
SUMMARY OF THE INVENTION
The objects of this invention are provided by a process for the separation
of methylene chloride from methyl formate or ethyl formate which entails
the use of certain organic compounds as the agent in extractive
distillation.
DETAILED DESCRIPTION OF THE INVENTION
We have discovered that certain organic compounds will effectively increase
the relative volatility between methylene chloride and methyl formate or
ethyl formate and permit the separation of methylene chloride from methyl
formate or ethyl formate by rectification when employed as the agent in
extractive distilation. Table 2 lists the agents that we have found to be
effective extractive distillation agents to recover methylene chloride
from methyl formate. The data in Tables 2, 4 and 5 was obtained in a
vapor-liquid equilibrium still. In every case, the starting mixture was
the methylene chloride - methyl formate or ethyl formate azeotrope. The
relative volatilities are listed for each the agents investigated. The
compounds which are effective extractive distillation agents to remove
methylene chloride from methyl formate are methyl acetate, ethyl acetate,
isopropyl acetate, n-propyl acetate, n-butyl acetate, isobutyl acetate,
isoamyl acetate, n-amyl acetate, ethylene glycol methyl ether acetate,
4-methyl-2-pentanone, 3-pentanone, mesityl oxide, 3-hexanone, 2-hexanone,
ethyl butyl ketone, 2-methyl pentanone, 3,3-dimethyl-2-butanone, methyl
isoamyl ketone, propylene glycol dimethyl ether and 3-methyl-1-butanol.
n-Butyl acetate whose relative volatility had been determined in the
vapor-liquid equilibrium still was then evaluated in a glass perforated
plate rectification column possessing 7.3 theoretical plates and the
results listed in Table 3. After two hours of continuous operation a
relative volatility for n-butyl acetate of 2.0 was obtained.
Table 4 lists the agents that we have found to be effective extractive
distillation agents to recover methylene chloride from ethyl formate. They
are n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate,
hexyl acetate, isobornyl acetate, ethylene glycol ethyl ether acetate,
2-hexanone, mesityl oxide, 3,3-dimethyl-2-butanone, ethyl butyl ketone,
3-methyl-2-butanone, 3-hexanone, 2-heptanone, diisobutyl ketone, methyl
isoamyl ketone, 2,4-pentanedione, diacetone alcohol, propoxypropanol,
butoxypropanol, propylene glycol methyl ether, propyl butyrate, dibutyl
ether, diethylene glycol t-butyl methyl ether, nitromethane,
1-nitropropane and 2-nitropropane.
Table 5 lists a number of compounds that proved to be ineffective as
extractive distillation agents in the separation of methylene chloride
from ethyl formate.
TABLE 2
______________________________________
Effective Agents for Separating
Methylene Chloride From Methyl Formate
Relative
Compounds Volatility
______________________________________
Methyl acetate 2.75
Ethyl acetate 1.7
Isopropyl acetate 2.3
n-Propyl acetate 1.85
4-Methyl-2-pentanone 1.95
3-Pentanone 2.0
n-Butyl acetate 2.0
Isobutyl acetate 1.8
Mesityl oxide 2.0
3-Hexanone 2.0
2-Hexanone 1.95
3-Methyl-1-butanol 1.5
Ethyl butyl ketone 2.1
3,3-Dimethyl-2-butanone
1.9
2-Methyl pentanone 1.65
Isoamyl acetate 2.1
n-Amyl acetate 2.8
Propylene glycol dimethyl ether
1.8
Ethylene glycol methyl ether acetate
1.75
Methyl isoamyl ketone 1.8
______________________________________
TABLE 3
__________________________________________________________________________
Data From Run Made In Rectification
Column - Methylene Chloride - Methyl Formate
Time
Weight %
Weight %
Relative
Agent Column
hrs.
CH.sub.2 Cl.sub.2
MeForm
Volatility
__________________________________________________________________________
n-Butyl acetate
Overhead
1 96.7 3.3 1.3
Bottoms 69.3 30.7
" Overhead
2 99.8 0.2 2.0
Bottoms 78.3 21.7
__________________________________________________________________________
Isobornyl acetate whose relative volatility had been determined in the
vapor-liquid equilibrium still was then evaluated in the glass perforated
plate rectification column possessing 7.3 theoretical plates and the
results listed Table 6. After two hours of continuous operation, a
relative volatility for isobornyl acetate of 1.4 was obtained.
THE USEFULNESS OF THE INVENTION
The usefulness or utility of this invention can be demonstrated by
referring to the data presented in Tables 2 to 6. All of the successful
agents show that methylene chloride can be separated from methyl formate
or ethyl formate by extractive distillation in a rectification column and
that the ease of separation as measured by relative volatility is
considerable.
TABLE 4
______________________________________
Effective Agents For Separating
Methylene Chloride From Ethyl Formate
Relative
Compounds Volatility
______________________________________
n-Butyl acetate 1.25
Isobutyl acetate 1.35
n-Amyl acetate 1.3
Isoamyl acetate 1.35
Ethylene glycol ethyl ether acetate
1.7
Isobornyl acetate 1.55
2-Hexanone 1.7
Mesityl oxide 1.25
3,3-Dimethyl-2-butanone
1.25
3-Methyl-2-butanone 1.55
Ethyl butyl ketone 1.25
3-Hexanone 1.75
2-Heptanone 1.65
Diisobutyl ketone 1.5
Methyl isoamyl ketone 1.5
2,4-Pentanedione 1.7
Diacetone alcohol 3.3
Propoxypropanol 1.9
Butoxypropanol 1.5
Propylene glycol methyl ether
1.75
Hexyl acetate 1.25
Propyl butyrate 1.35
Dibutyl ether 1.9
Diethylene glycol t-butyl methyl ether
1.35
Nitromethane 2.5
1-Nitropropane 1.8
2-Nitropropane 2.0
______________________________________
TABLE 5
______________________________________
Ineffective Agents For Separating
Methylene Chloride From Ethyl Formate
______________________________________
3-Pentanone Ethylene glycol methyl ether acetate
Vinyl butyl ether
Ethylene glycol butyl ether acetate
Nitroethane 2-Methoxyethyl acetate
Methyl vinyl acetate
______________________________________
TABLE 6
__________________________________________________________________________
Data From Run Made In Rectification
Column - Methylene Chloride - Ethyl Formate
Time
Weight %
Weight &
Relative
Agent Column
hrs.
CH.sub.2 Cl.sub.2
EtFormate
Volatility
__________________________________________________________________________
Isobornyl acetate
Overhead
1 97.2 2.8 1.23
Bottoms 88.6 11.4
" Overhead
2 98.1 1.9 1.40
Bottoms 88.2 11.8
__________________________________________________________________________
WORKING EXAMPLES
EXAMPLE 1
Eighty grams of the methylene chloride - methyl formate azeotrope and 30
grams of n-butyl acetate were charged to a vapor-liquid equilibrium still
and refluxed for three hours. Analysis indicated a vapor composition of
89.9% methylene chloride, 10.1% methyl formate; a liquid composition of
79.5% methylene chloride, 20.5% methyl formate which is a relative
volatility of methylene chloride to methyl formate of 2.3.
EXAMPLE 2
A solution comprising 40 grams of methylene chloride and 160 grams of
methyl formate was placed in the stillpot of a 7.3 theoretical plate
rectification column. When refluxing began, an extractive agent comprising
n-butyl acetate was pumped into the column at a rate of 15 ml/min. The
temperature of the extractive agent as it entered the column was
85.degree. C. After establishing the feed rate of the extractive agent,
the heat input to the methylene chloride - methyl formate in the stillpot
was adjusted to give a total reflux rate of 40 ml/min. After two houss of
operation, the overhead and bottoms samples of approximately two ml. were
collected and analysed. The overhead analysis was 99.8% methylene
chloride, 0.2% methyl formate and the bottoms analysis was 78.3% methylene
chloride, 21.7% methyl formate. This gives an average relative volatility
of 2.0 for each theoretical plate. This data is presented in Table 3.
EXAMPLE 3
Eighty grams of the methylene chloride - ethyl formate azeotrope and 30
grams of isobornyl acetate were charged to the vapor-liquid equilibrium
still and refluxed for five hours. Analysis indicated a vapor composition
of 94.5% methylene chloride, 5.5% ethyl formate; a liquid composition of
91.4% methylene chloride, 8.6% ethyl formate which is a relative
volatility of methylene chloride to ethyl formate of 1.55.
EXAMPLE 4
A solution comprising 184 grams of methylene chloride and 16 grams of ethyl
formate was placed in the stillpot of the 7.3 theoretical plate
rectification column. When refluxing began, an extractive agent comprising
isobornyl acetate was pumped into the column at a rate of 15 ml/min. The
temperature of the extractive agent as it entered the column was
85.degree. C. After establishing the feed rate of the extractive agent,
the heat input to the methylene chloride - ethyl formate in the stillpot
was adjusted to give a total reflux rate of 40 ml/min. After two hours of
operation, the overhead analysis was 98.1% methylene chloride, 1.9% ethyl
formate and the bottoms analysis was 88.2% methylene chloride, 11.8% ethyl
formate. This gives an average relative volatility of 1.4 for each
theoretical plate. This data is presented in Table 6.
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